In recent years, scores of educators and designers have been won over to the view that natural light — provided by the sun instead of bulbs or tubes — is desirable and beneficial for education facilities.
Studies that show students performing better in classrooms that have the right kinds of daylighting bear out the intuitive beliefs of many teachers that a classroom with natural light is a more appealing learning climate. Daylight also enables schools to trim their utility bills by becoming less dependent on electricity and artificial light.
But acknowledging that daylighting benefits schools won't transform every classroom with a window into an ideal learning environment.
For daylighting to have the desired effect on learning and energy costs, designers and educators must plan carefully. There are different kinds of daylight and different ways to bring it into a school. Choosing the right footprint for a facility, selecting the right kinds of windows — how many, how large, what shape, how they are arranged, what types of materials are used — and picking building systems that maximize the effectiveness of daylighting are key to creating an energy-efficient space where students learn more effectively.
The appeal of daylighting in school facilities has grown since a 1999 study by the Heschong Mahone Group, a California consulting firm. The study looked at classrooms in the Capistrano School District and found that students with the most daylighting in their classrooms progressed 20 percent faster on math tests and 26 percent faster on reading tests than students exposed to the least daylighting.
It also found that students in classrooms with a well-designed skylight improved their test scores 19 to 20 percent faster than those students without a skylight. A well-designed skylight was defined as “one that diffused the daylight throughout the room and which allowed teachers to control the amount of daylight entering the room.” Ineffective skylights — ones that allowed direct sunlight into a room and caused glare — negatively affected student performance.
The U.S. Department of Energy's National Best Practices Manual for Building High-Performance Schools says that direct sunlight should be allowed to enter a space only in small quantities and only in areas where people are not required to work.
“Good daylighting design typically relies on maximizing the use of gentle, diffuse daylight and minimizing the penetration of direct beam sunlight,” the manual says.
In a design brief on daylighting, Energy Design Resources, a program developed by Southern California Edison, identifies six design principles to follow when developing a daylighting design:
Think of the building as a luminaire, or a lighting fixture
“As with any lighting fixture, internal and external geometries and finishes play an important role in how light is distributed,” the brief says.
Separate the vision and the daylight glazings
“Glazing serves two different purposes: providing a view out and allowing daylight in,” the brief states. Vision glazings typically let less light in to allow comfortable views to the outside without resorting to blinds or other vision controls. Daylight glazings are used primarily to provide interior illumination.
“Generally, daylight glazings are located about the occupants' heads,” the brief says. “Fenestration control (either internal or external light shelves or shading elements) is required to prevent direct view of daylighting apertures.”
Create mood and focus
“Careful attention to aperture location and detailing can greatly influence the directionality and placement of daylight,” states the brief.
Address the requirements of the visual task
“The quantity and directionality of light provided by the daylighting system should be appropriate for the visual task,” the brief says.
Integrate the daylighting system with the architecture
“The use of daylight … can provide the foundation for a unique building design,” says the brief.
Integrate the building system with other building systems
“The presence of daylight should influence the design of the electric lighting and control systems,” the brief states.
In the right direction
Orienting a building footprint and the fenestration openings will enable a facility to take advantage of daylight.
“It is easiest to provide excellent daylight conditions using north-facing windows, since the sun only strikes a north-facing window in early morning and late evening during midsummer,” the Best Practices Manual says. “South-facing windows are the next best option because the high angle of the south sun can be easily shaded with a horizontal overhang. East- and west-facing windows are more problematic because when the sun is low in the sky, overhangs or other fixed shading devices are of limited utility.”
The daylight will reflect off walls and ceilings, so those surfaces should be white or a very light color to prevent the daylight from being absorbed.
Daylighting strategies can be divided into two categories: sidelighting and toplighting. Sidelighting admits light from the perimeter walls of a building. “For buildings with long, shallow floor geometries, it is feasible to daylight up to 70 percent of the footprint with a sidelighting system,” the Energy Design Resources brief states.
For sidelighting to be effective, a ceiling must be at least 9 feet high; 10 feet or higher is recommended. “Internal daylight control elements are needed to reflect and redirect light from the daylight glazings to the ceiling plane,” the brief says.
Toplighting admits light through the top of a building and can have either vertical or horizontal glazing. “Toplighting strategies generally fall into the broad categories of roof monitors, clerestories, sawtooth elements, skylights and atria,” the brief says.
To make sure that a daylighting design saves energy, schools should choose efficient window systems that minimize solar heat gain and have an electric lighting system that responds to the need for artificial light.
“The benefits from daylighting are maximized when both occupancy and light sensors are used to control the electric lighting system,” says the Department of Energy's Office of Energy Efficiency and Renewable Energy. “With these two control strategies, the lights will come on only when the room is occupied and only if there is insufficient daylight.”
Sidebar: Daylight in Chilton
Completed in 2003, the new Chilton High School in Chilton, Wis., relies heavily on daylighting for its energy performance. According to the Daylighting Collaborative, a program started by utilities and the State of Wisconsin to incorporate daylighting into design and construction, the 186,344-square-foot school has more than 4,700 square feet of exterior glass.
Classrooms along the perimeter of the building receive natural light from windows along exterior walls, and daylight reaches classrooms on the interior of the facility through the use of clerestory windows.
The windows have differing degrees of tinting to maximize the effects of natural light.
“The glass on the north side of the building is not tinted as dark as the glass on the east, south or west sides,” the collaborative states.
To further reduce the dependency on electric lighting, occupancy sensors have been installed throughout the school. They are programmed to adjust to the differing building usage on weekends and in the summer.
20 to 30%
Preferred visible transmittance value for vision glass.
50 to 60%
Preferred visible transmittance value for daylighting glass.
Source: Energy Design Resources, “Design Brief: Daylighting”
Kennedy, staff writer, can be reached at [email protected].